Skin cancer occurs when errors (mutations) form the in the DNA of healthy skin cells. The mutations cause the cells to grow out of control and form a mass of cancer cells. Skin cancer begins in your skin's top layer—the epidermis. The epidermis is a thin layer that provides a protective cover of skin cells that your body continually sheds. The epidermis contains three main types of cells:                Squamous cells lie just below the outer surface and function as the skin's inner lining.        Basal cells, which produce new skin cells, sit beneath the squamous cells.        Melanocytes—which produce melanin, the pigment that gives skin its normal color—are located in the lower part of your epidermis. Melanocytes produce more melanin when you're in the sun to help protect the deeper layers of your skin. Extra melanin produces the darker color of tanned skin.        